1. Field of the Invention
The present invention relates to a waveform correction apparatus and a waveform correction method. For example, the present invention relates to a waveform correction apparatus and a waveform correction method used in a position detector detecting a moving body making a rotational movement or a reciprocating movement.
2. Related Art
Generally, a rotary encoder is used as a position detector detecting a position of a moving body (e.g., a servo motor) making a rotational movement, or a linear scale is used as a position detector detecting a position of a moving body making a linear reciprocating movement. An output signal from the position detector is periodically subjected to analog-digital conversion (sampling), converted into a Value indicating an angle or the position, and the resultant digital signal is used. To accurately detect the angle or the position of the moving body, it is necessary to remove offsets of digital signals (a sin signal and a cos signal) obtained by the sampling, and to correct amplitudes of the sin signal and the cos signal to reference values, respectively.
Conventionally, an operator makes the digital signal Correction visually. Specifically, the sin signal and the cos signal are input to a synchroscope and a circle called “Lissajous figure” is displayed on an X-Y plane. The operator adjusts an output circuit or an input circuit while observing a position and a magnitude of the Lissajous figure by the naked eye so as to remove offsets and to correct amplitudes of the signals. This is a normalization operation for the sin signal and the cos signal. The “normalization” is to adjust the Lissajous figure obtained by sampling into a shape according to a predetermined standard.
Needless to say, if the sin signal and the cos signal are to be normalized visually, it is necessary to obtain the synchroscope and manpower. This results in cost increase and longer time. Furthermore, because of visual normalization, it is difficult for even a skilled person to normalize the signals with high accuracy. This disadvantageously causes deterioration in position detection accuracy or velocity detection accuracy.
If an internal response rate of the output circuit of the position detector is low, a voltage width (slew rate) changeable per unit time in the position detector is small. Accordingly, if frequencies of input and output signals to or from the position detector are higher, the phenomenon occurs that amplitudes of the cos signal and the sin signal dynamically fall. In this case, the cos signal and the sin signal cannot be normalized visually.
Therefore, it is an object of the present invention to provide a waveform correction circuit and a waveform correction method capable of correcting a digital signal obtained by sampling a waveform signal at low cost, at high rate, and with high accuracy.